1. Field of the Invention
The present invention relates generally to a mobile communication system, and in particular, to a method for scheduling data packet transmission in a mobile communication system supporting time division multiplexing (TDM) for a shared link.
2. Description of the Related Art
A 3rd generation mobile communication system includes CDMA2000 (Code Division Multiple Access 2000), WCDMA/UMTS (Wideband CDMA/Universal Mobile Telecommunications System), GPRS (General Packet Radio System), and CDMA2000 1xEV-DO (Evolution Data Only) mobile communication systems. Unlike the typical 2nd generation mobile communication system supporting only a voice service or a low-speed data service, the 3rdgeneration mobile communication system supports the voice service and also a high-speed packet data service and a moving picture communication service. The mobile communication system includes a base station controller (BSC), a base transceiver system (BTS), and a mobile station (MS). The BSC is connected to the BTS by wire, and the BTS is connected to the MS through a radio channel.
In the mobile communication system, when the BSC communicates with a specified MS among a plurality of MSs through the BTS, the BSC sequentially transmits transmission data packets to the BTS to which the specified MS belongs. The BTS then buffers (or stores) the received data packets in its buffer, and sequentially transmits the buffered data packets to the specified MS for a time period where a radio resource is available. A technique for sharing one radio resource, or one transmission channel, by a plurality of MSs is called “time division multiplexing (TDM).”
In a mobile communication system transmitting data packets by the TDM, determining a time period for which the data packets are transmitted to MS is called “scheduling,” and radio resources of BTS are properly assigned to a plurality of MSs by the scheduling. A scheduler for the scheduling operation exists in BTS, and the MS periodically reports the quality of a BTS signal received over a radio channel to the scheduler. The scheduler selects a particular MS, to which it will transmit data, every scheduling period, taking into account quality information of radio channels received from a plurality of MSs and an absence/presence of data to be transmitted to each MS.
A data service in the conventional mobile communication system is based on the so-called “best effort service.” That is, a condition of a data service provided to a particular mobile subscriber (or MS) is determined based on a radio channel quality of the subscriber and availability of a radio resource with which each BTS services subscribers. Therefore, if an amount of service data provided by one BTS to other subscribers, not including the particular subscriber, is increased or a radio channel quality of the corresponding subscriber becomes worse, then an amount of data provided to the subscriber is decreased.
However, a certain subscriber may want to secure a better service quality, or a higher data rate, at any cost. In addition, a service provider may also want to provide a better service quality to a particular subscriber, for example, a long-term subscriber. However, as stated above, in providing a packet data service, the conventional mobile communication system considers only the quality of a radio channel and the availability of radio resources, and does not consider service requirements of the subscriber. Therefore, in order to provide a service quality on a level requested by the subscriber, it is necessary to provide differential services according to a QoS (Quality of Service) class.